Traditionally, the use of electric submersible pumps (ESPs) in slurries suffers due to the tendency of solid materials within the slurry settling to the bottom of the tank, rather than remaining sufficiently suspended in the fluid in order to be picked up and carried out by the pump. In extreme situations, often encountered for example in steel mills, the use of ESPs in slurry ponds may often necessitate frequent shutdown of the mill's operations while an excavator is moved into the pits to remove the material accumulated at the bottom of the pit. In addition, significant problems with respect to the erosion of mechanical equipment (such as the pumps and the associated agitators) occur when these devices are used to pump thick slurry mixtures, due to abrasive contact between the solids within the slurry and the portions of the mechanical equipment submerged in the slurry. The cause of the erosion is due largely in part to the high abrasiveness of the pumped fluids which contain relatively heavy, solid particulates in the mixture (hereinafter referred to as slurries). In making its way through the pump mechanism, the slurries cause erosion of the impeller blades or vanes (herein referred to interchangeably as blades and vanes), which ultimately leads to wear on the pump mechanism, volute casing and stator of the pump, leading to loss of performance, and possibly subsequent inoperability, of the pump where sustained erosion has occurred. Ongoing wear on the vanes and other portions of the pump may cause significant downtime for repairs and replacements, leading to inefficiencies resulting higher pump maintenance costs and more frequent pump failures or pump repairs.
In many applications, the pumps will be pumping solids that are settled on the floor of a sump. The pump's agitator assists in suspending those solids so they will be picked up for pumping. Thus, agitators are presently known and used to suspend solids in the slurry prior to the slurry being entrained into the impeller, especially where solids have settled out, for example on the floor of a sump. The purpose of an agitator is to mix solids to ensure a mixture containing suspended solids, so that the solids may be pumped through the impeller along with the liquids in which the solids are suspended.
One form of agitator employs vanes mounted below, or otherwise upstream, of the impeller intake, driven from the impeller drive shaft. Thus, rotation of the impeller vanes also rotates the agitator vanes. Conventional agitators of this form, in submersible pumps, use shaft-mounted agitator vanes to force the slurry in which the pump is submersed through the agitator channels between the vanes, as the shaft and vanes are rotated about the shaft's axis of rotation. The rotation of the vanes in the slurry urges the slurry from the agitator channels or passageways so as to agitate the slurry for pumping, while mixing the slurry so as to suspend the solids in the slurry.
As mentioned above, a drawback of pumping slurries containing suspended solids, such as sand, slate and mill scale, is that the suspended solids abrade the agitator vanes. Typical abrasion will, in the Applicant's experience, shorten the life-span of the vanes, for example by thinning the vanes so that they eventually fail and break off of the shaft under load. To extend the life of the vanes, and thereby extend the periods of time the pump may be in service before requiring to be pulled for inspection and servicing, conventionally the vanes are relatively thick and have a restricted depth, measured as the dimension through the vane perpendicular to the axis of rotation of the drive shaft. However, the thicker the vanes and more restricted the depth of the vanes, the less efficient is a set of vanes for agitating a slurry prior to entrainment into the impeller.
Consequently, there exists a need for improved agitator vanes that have an optimal blade shape, for example, optimal curvature and depth so as to optimize volumetric output and velocity of the slurry being pushed downwardly by the agitator.
Applicant is aware of the United States Patent Application No. US 2014/0112755 entitled “Pumps” and U.S. Pat. No. 8,622,706 entitled “Slurry pump having impeller flow elements and a flow directing device”, each granted to Burgess. Burgess discloses a pump assembly including a pump impeller, where the impeller includes: a hub, a back shroud extending from the hub, and a front shroud. Each of the shrouds has an inner surface and an outer surface. A plurality of pumping vanes extends between the respective inner surfaces of the shrouds. An impeller inlet opening in the front shroud is coaxial with the rotation axis of the impeller. The impeller includes one or more elements which extend from the inner surface of the front shroud towards the rotation axis and which are positioned adjacent the impeller inlet opening. A flow directing device directs material in relation to the adjacent moving impeller.
In applicant's experience, the pump described by Burgess would not achieve the improved performance of the agitator of the present disclosure, and would not solve the above identified vane wear issues due to abrasion of the vanes. Burgess discloses that the vanes extend between the respective inner surfaces of the shrouds; thus, when the Burgess agitator wears out, the whole impeller needs replacing to replace the agitator.